The present invention relates to a novel chiral smectic C liquid crystalline polyester having large spontaneous polarization, capable of forming a stable smectic C liquid crystal in a wide temperature range and being subjected to melt-molding, and suitable for use in the field of optoelectronics and in the optical field.
Since liquid crystals have a specific order of the molecular orientation peculiar to them, they can be used in various fields by utilizing or controlling their molecular orientation, thus forming a great industrial field. As to lowmolecular liquid crystals, as well known, those of nematic type are in wide use as display elements for watches, desk-top electronic calculators or televisions and they occupy an immovable position in the display field. Recently, moreover, chiral smectic C liquid crystals having characteristic features such as high-speed operation and memory function have been noted as liquid crystals for the display elements of the next generation which will take the place of the nematic ones referred to above. And now there is keen competition for the development thereof.
On the other hand, as to high-molecular liquid crystals, it is well known that they exhibit electrooptical effects or thermooptical effects similar to those of the low-molecular liquid crystals according to the types of them, i.e., nematic, smectic and cholesteric types, not to mention their excellent mechanical characters. The response of the high-molecular liquid crystals to an external force such as an electric field and heat is slower than that of the low-molecular ones because of their high viscosity, but basically they have the same properties as the properties of the low-molecular liquid crystals. Further, the orientation structure peculiar to each type of the high-molecular liquid crystals can be fixed, and the high-molecular liquid crystals permit easy formation of a flexible film having a large area. These are great characteristic features not found in the low-molecular liquid crystals.
Therefore, if a high polymer which exhibits chiral smectic C liquid crystallinity can be prepared, it will have the same function as that of the low-molecular chiral smectic C liquid crystals, which liquid crystallinity can be fixed, and it will afford a material having a large area and easy to handle, so it can be applied to various uses in the fields of display materials, recording materials and optical materials. However, there is scarcely known any polymer which exhibits clear chiral smectic C liquid crystallinity and which permits fixing thereof. For example, J. C. Dubois et al. reported polyacrylic ester derivatives having a structure of the following formula in which the side chain has a mesogen containing a chiral unit [Mol. Cryst. Liq. Cryst., 137, 349 (1986)]: ##STR3##
According to X-ray diffractometry of polymers of the above formula wherein R is H and n is 2, R is CH.sub.3 and n is 11, or R is Cl and n is 11, Dubois et al. found that the polymers had a smectic layer structure and that the major axis of the mesogen of the side chain was inclined relative to the normal. From these facts they suggested the possibility of these polymers forming a phase looking like chiral smectic C in a certain temperature range. However, no report has been made by them on the results of optical observation or pitch length, and the formation of the chiral smectic C phase has not been proved clearly by them, with no report on the fixation, either. Further, the preparation of the monomer having such a side chain requires a multiple step operation and is extremely troublesome.
In addition, V. P. Shibaev. et al. reported polyacrylic ester derivatives similar to those described above [Polymer Bulletin 12, 299 (1984)]: ##STR4## wherein m represents a number of 6 to 12 and no definition is given to R, R.sub.1 and R.sub.2.
According to X-ray diffractometry, Shibaev et al. found that these derivatives had a smectic layer structure, that the major axis of the mesogen of the side chain was inclined relative to the normal and that spontaneous polarization was observed. From these facts they concluded that the polymers form a chiral smectic C liquid crystal phase However, the structure of the Shivaev et al.'s polymers has not been made clear; besides, like the polymers of Dubois et al., the preparation of the Shivaev et al.'s polymers is extremely troublesome and an industrial preparation thereof encounters difficulties. And no report has been made by them about fixation. Further, these polymers of the polyacrylic acid derivative type are produced by introducing the low-molecular chiral smectic C liquid crystals as they are into the side chain thereof. In this sense it can be said that they lie on the extension of the low-molecular liquid crystals. On the other hand, high-molecular liquid crystals of the main chain type containing a chiral component in the main chain and being clear chiral smectic C liquid crystals are not known at all. Although the production of polyesters and polyamides containing a chiral component in the main chain thereof has been reported, the products are mostly cholesteric liquid crystals. Further, although there are some examples of nematic and smectic liquid crystals produced, no reports have been made about products having a distinct chiral smectic C phase.